Weyl and Nodal Ring Magnons in Three-Dimensional Honeycomb Lattices**Supported by the National Basic Research Program of China under Grant No 2015CB921300, the National Natural Science Foundation of China under Grant No 11334012, and the Strategic Priority Research Program of Chinese Academy of Sciences under Grant No XDB07000000.

Abstract

We study the topological properties of magnon excitations in a wide class of three-dimensional (3D) honeycomb lattices with ferromagnetic ground states. It is found that they host nodal ring magnon excitations. These rings locate on the same plane in the momentum space. The nodal ring degeneracy can be lifted by the Dzyaloshinskii–Moriya interactions to form two Weyl points with opposite charges. We explicitly discuss these physics in the simplest 3D honeycomb lattice and the hyperhoneycomb lattice, and show drumhead and arc surface states in the nodal ring and Weyl phases, respectively, due to the bulk-boundary correspondence.